Biosolids beneficial-use programs effectively recycle plant nutrients when biosolids are applied at agronomic rates. Determining such rates to overgrazed western US rangelands can be challenging in terms of applying adequate plant N, increasing biomass production and species diversity, and improving soil quality. New York City biosolids were applied once to an overgrazed rangeland near Lamar, Colorado at rates of 0, an “agronomic rate” (2-4), 10, 21, and 44 Mg/ha to determine the effects on biomass production, protein and nutrient content, species enrichment, soil nutrient/trace metal content, and water infiltration rates. Biosolids were applied in 1999. Plant samples were obtained in 2000 through 2005. Soil samples were obtained in 2003 and analyzed for AB-DTPA extractable trace metals. Soil characteristics related to water infiltration were collected in 2006.

Biomass increased with increasing biosolids application up to 21 Mg/ha, after which biomass decreased. The number of species present, plant protein, P, Zn, Cu, and Mn content increased with increasing biosolids rate. Phosphorus, Zn, and Mn concentrations were below the maximum tolerable levels for domestic livestock dietary intact; plant Cu content in 2000, 2001, and 2003 were above these levels for cattle and sheep. However, plant Cu content tended to decrease with time. Soil AB-DTPA extractable metal concentrations were all near or below detection limits. Soil porosity and bulk density did not change across treatments. However, increasing biosolids application increased soil saturated hydraulic conductivity and moisture holding capacity. Results validate research findings from several institutions.